Patterning device support, lithographic apparatus, and method of controlling patterning device temperature

ABSTRACT

A patterning device support for controlling a temperature of a patterning device can include a movable component. The movable component can include a gas inlet for supplying a gas flow across a surface of the patterning device and a gas outlet for extracting the gas flow. The patterning device support can also include a gas flow generator coupled to a duct, for recirculating the gas flow from the gas outlet to the gas inlet.

This application incorporates by reference in their entireties U.S.patent application Ser. No. 15/438,376, filed Feb. 21, 2017, U.S. patentapplication Ser. No. 14/439,359, 371(c) Date: Apr. 29, 2015, Int'l Appl.No. PCT/EP2013/071933, filed Oct. 21, 2013, U.S. Provisional ApplicationNo. 61/768,125, filed Feb. 22, 2013, U.S. Provisional Application No.61/752,751, filed Jan. 15, 2013, U.S. Provisional Application No.61/720,628, filed Oct. 31, 2012, and U.S. Provisional Patent ApplicationNo. 61/836,336, filed Jun. 18, 2013, which are all incorporated hereinin their entireties by reference.

BACKGROUND Field

Embodiments of the present invention generally relate to apparatuses forsupporting a patterning device of a lithographic apparatus and, moreparticularly, to apparatuses and methods for controlling the temperatureof a patterning device by flowing gas across a surface of the patterningdevice.

Related Art

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, to manufactureintegrated circuits (ICs). In such a case, a patterning device, forexample, a mask or a reticle, can generate a circuit pattern to beformed on an individual layer of the IC. This pattern can be transferredonto a target portion (for example, including part of, one, or severaldies) on a substrate (for example, a silicon wafer). Transfer of thepattern is typically via imaging onto a layer of radiation-sensitivematerial (resist) provided on the substrate. Generally, a singlesubstrate will contain a network of adjacent target portions that aresuccessively patterned. Conventional lithographic apparatuses includeso-called steppers, in which each target portion is irradiated byexposing an entire pattern onto the target portion at once, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

The patterning device can comprise a base material, for example, fusedsilica, that is substantially transparent to radiation, for example,deep ultraviolet radiation, and comprise a pattern made of asubstantially non-transparent material, for example, chrome. Typically,the pattern absorbs the radiation, which generates heat. This heatcauses the patterning device to expand and can adversely affect the airbetween the patterning device and proximal lens elements. For example,patterning device expansion can cause image distortion (such as overlayerrors). Reticle or wafer alignment, magnification correction, feedforward systems for expansion prediction, and lens correction canpartially address such image distortion. But these correction methods donot reduce imaging errors due to heating of the air between thepatterning device and the lens element, so as tighter tolerances arerequired, these correction methods may not adequately address imagedistortion caused by the patterning device thermal expansion.

SUMMARY

In some embodiments, a system to control a temperature of a patterningdevice in a lithographic apparatus comprises a patterning devicesupport. The patterning device support comprises a movable component,for example, a short stroke module, configured to support the patterningdevice and to move during operational use. The movable component definesa first opening adjacent a first end of a first surface of thepatterning device. The patterning device support also comprises a gasinlet configured to provide a gas flow across the first surface of thepatterning device. The gas inlet passes through the first opening of themovable component and has an opening adjacent the first end of the firstsurface of the patterning device. The patterning device support alsocomprises a gas outlet having an opening configured to extract the gasflow. The opening of the gas outlet is adjacent a second end of thefirst surface of the patterning device. The gas inlet and the gas outletare configured such that the gas flow is substantially parallel to thefirst surface of the patterning device. The gas flow affects thetemperature of the patterning device.

In some embodiments, a lithographic system comprises a patterning devicesupport comprising a movable component, for example, a short strokemodule, configured to support a patterning device. The system alsoincludes a gas inlet disposed adjacent to and spaced from the movablecomponent. The gas inlet is configured to supply a gas for forming a gasflow across a first surface of the patterning device to affect thetemperature of the patterning device. The gas inlet is configured tomove with the patterning device during operational use. The system alsocomprises a gas outlet disposed above the movable component and thepatterning device. The gas outlet is configured to be stationary duringoperational use.

In some embodiments, a patterning device support for controlling atemperature of a patterning device includes a movable componentconfigured to move the patterning device. The movable component caninclude a gas inlet for supplying a gas flow across a surface of thepatterning device and a gas outlet for extracting the gas flow. Themovable component can include a gas flow generator configured torecirculate the gas flow and a duct for passing the gas flow from thegas outlet to the gas inlet.

In some embodiments, a lithographic apparatus can include anillumination system configured to condition a radiation beam. Thelithographic apparatus can also include a patterning device support forcontrolling a temperature of a patterning device. The patterning devicesupport includes a gas inlet for supplying a gas flow across a surfaceof the patterning device and a gas outlet for extracting the gas flow.The patterning device support can also include a duct for recirculatingthe gas flow from the gas outlet to the gas inlet. The lithographicapparatus can also include a substrate table constructed to hold asubstrate, and a projection system configured to project the patternedradiation beam onto a target portion of the substrate.

In some embodiments, a lithographic apparatus can include a patterningdevice support and movable component comprising a gas inlet configuredto supply a gas flow across a surface of the patterning device, a gasoutlet configured to extract the gas flow, and a duct configured torecirculate the gas flow from the gas outlet to the gas inlet. Thelithographic apparatus can also include a controller configured toadjust a first characteristic of the gas flow to achieve a desiredtemperature of the patterning device.

In some embodiments, a method for controlling a temperature of apatterning device includes flowing a gas across a surface of thepatterning device from a gas inlet of a patterning device support to agas outlet of the patterning device support or of a fixed plate abovethe patterning device support. The method can also include recirculatingthe gas from the gas outlet to the gas inlet.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIG. 1A is a schematic illustration of a reflective lithographicapparatus according to an embodiment.

FIG. 1B is a schematic illustration of a transmissive lithographicapparatus according to an embodiment.

FIGS. 2A and 2B are schematic illustrations of a side view of apatterning device support and a fixed plate above the patterning devicesupport according to embodiments.

FIG. 3 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 4 is a schematic illustration of a side view of a patterning devicesupport according to an embodiment.

FIGS. 5A and 5B are schematic illustrations of a side view of apatterning device support according to embodiments.

FIG. 6 is a schematic illustration of an exemplary infrastructureaccording to an embodiment.

FIG. 7A is a schematic illustration of a side view of a patterningdevice support according to an embodiment.

FIG. 7B is a schematic illustration of an enlarged portion of thepatterning device support of FIG. 7A.

FIG. 8 is a schematic illustration of a side view of a patterning devicesupport according to an embodiment.

FIG. 9 is a flow diagram of a method of cooling a patterning deviceaccording to an embodiment.

FIG. 10 is a flow diagram of a method of cooling a patterning deviceaccording to an embodiment.

FIG. 11 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 12 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 13 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 14 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 15 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 16 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 17 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 18 is a schematic illustration of a top view of a patterning devicesupport according to an embodiment.

FIG. 19 is a schematic illustration of a side view of a patterningdevice support according to an embodiment.

FIG. 20 illustrates computer system hardware useful in implementing theembodiments shown in FIGS. 1A through 6.

FIG. 21 is a schematic illustration of an exemplary infrastructureaccording to an embodiment.

FIG. 22 is a schematic illustration of an exemplary infrastructureaccording to an embodiment.

The features and advantages of the disclosed embodiments will becomemore apparent from the detailed description set forth below when takenin conjunction with the drawings.

DETAILED DESCRIPTION OF THE INVENTION

This specification discloses one or more embodiments that incorporatethe features of this invention. The disclosed embodiment(s) merelyexemplify the invention. The scope of the invention is not limited tothe disclosed embodiment(s). The invention is defined by the claimsappended hereto.

The embodiment(s) described, and references in the specification to “oneembodiment,” “an embodiment,” “an example embodiment,” “someembodiments,” etc., indicate that the embodiment(s) described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is understood that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Before describing such embodiments in more detail, however, it isinstructive to present an example environment in which embodiments ofthe present invention may be implemented.

Example Reflective and Transmissive Lithographic Systems

FIGS. 1A and 1B are schematic illustrations of a lithographic apparatus100 and lithographic apparatus 100′, respectively, in which embodimentsof the present invention may be implemented. Lithographic apparatus 100and lithographic apparatus 100′ each include the following: anillumination system (illuminator) IL configured to condition a radiationbeam B (for example, DUV or EUV radiation); a support structure (forexample, a mask table) MT configured to support a patterning device (forexample, a mask, a reticle, or a dynamic patterning device) MA andconnected to a first positioner PM configured to accurately position thepatterning device MA; and, a substrate table (for example, a wafertable) WT configured to hold a substrate (for example, a resist coatedwafer) W and connected to a second positioner PW configured toaccurately position the substrate W. Lithographic apparatuses 100 and100′ also have a projection system PS configured to project a patternimparted to the radiation beam B by patterning device MA onto a targetportion (for example, comprising part of one or more dies) C of thesubstrate W. In lithographic apparatus 100, the patterning device MA andthe projection system PS are reflective. In lithographic apparatus 100′,the patterning device MA and the projection system PS are transmissive.In some embodiments, the projection system PS is catadioptric.

The illumination system IL may include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic, or other types of optical components, or any combinationthereof, for directing, shaping, or controlling the radiation B.

The support structure MT holds the patterning device MA in a manner thatdepends on the orientation of the patterning device MA, the design ofthe lithographic apparatuses 100 and 100′, and other conditions, such aswhether or not the patterning device MA is held in a vacuum environment.The support structure MT may use mechanical, vacuum, electrostatic, orother clamping techniques to hold the patterning device MA. The supportstructure MT can be a frame or a table, for example, which can be fixedor movable, as required. The support structure MT can ensure that thepatterning device is at a desired position, for example, with respect tothe projection system PS.

The term “patterning device” MA should be broadly interpreted asreferring to any device that can be used to impart a radiation beam Bwith a pattern in its cross-section, such as to create a pattern in thetarget portion C of the substrate W. The pattern imparted to theradiation beam B can correspond to a particular functional layer in adevice being created in the target portion C, such as an integratedcircuit.

The patterning device MA may be transmissive (as in lithographicapparatus 100′ of FIG. 1B) or reflective (as in lithographic apparatus100 of FIG. 1A). Examples of patterning devices MA include reticles,masks, programmable mirror arrays, and programmable LCD panels. Masksare well known in lithography, and include mask types such as binary,alternating phase shift, and attenuated phase shift, as well as varioushybrid mask types. An example of a programmable mirror array employs amatrix arrangement of small mirrors, each of which can be individuallytilted so as to reflect an incoming radiation beam in differentdirections. The tilted mirrors impart a pattern in the radiation beam Bwhich is reflected by the mirror matrix.

The term “projection system” PS can encompass any type of projectionsystem, including refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof, as appropriate for the exposure radiation being used, or forother factors, such as the use of an immersion liquid or the use of avacuum. A vacuum environment can be used for EUV or electron beamradiation since other gases can absorb too much radiation or electrons.A vacuum environment can therefore be provided to the whole beam pathwith the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus 100 and/or lithographic apparatus 100′ can be ofa type having two (dual stage) or more substrate tables WT (and/or twoor more mask tables). In such “multiple stage” machines, the additionalsubstrate tables WT can be used in parallel, or preparatory steps can becarried out on one or more tables while one or more other substratetables WT are being used for exposure.

Referring to FIGS. 1A and 1B, the illuminator IL receives a radiationbeam from a radiation source SO. The source SO and the lithographicapparatuses 100, 100′ can be separate entities, for example, when thesource SO is an excimer laser. In such cases, the source SO is notconsidered to form part of the lithographic apparatuses 100 or 100′, andthe radiation beam B passes from the source SO to the illuminator ILwith the aid of a beam delivery system BD (in FIG. 1B) including, forexample, suitable directing mirrors and/or a beam expander. In othercases, the source SO can be an integral part of the lithographicapparatuses 100, 100′—for example when the source SO is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD, if required, can be referred to as a radiation system.

The illuminator IL can include an adjuster AD (in FIG. 1B) for adjustingthe angular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to as“σ-outer” and “σ-inner,” respectively) of the intensity distribution ina pupil plane of the illuminator can be adjusted. In addition, theilluminator IL can comprise various other components (in FIG. 1B), suchas an integrator IN and a condenser CO. The illuminator IL can be usedto condition the radiation beam B to have a desired uniformity andintensity distribution in its cross section.

Referring to FIG. 1A, the radiation beam B is incident on the patterningdevice (for example, mask) MA, which is held on the support structure(for example, mask table) MT, and is patterned by the patterning deviceMA. In lithographic apparatus 100, the radiation beam B is reflectedfrom the patterning device (for example, mask) MA. After being reflectedfrom the patterning device (for example, mask) MA, the radiation beam Bpasses through the projection system PS, which focuses the radiationbeam B onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF2 (for example, aninterferometric device, linear encoder, or capacitive sensor), thesubstrate table WT can be moved accurately (for example, so as toposition different target portions C in the path of the radiation beamB). Similarly, the first positioner PM and another position sensor IF1can be used to accurately position the patterning device (for example,mask) MA with respect to the path of the radiation beam B. Patterningdevice (for example, mask) MA and substrate W can be aligned using maskalignment marks M1, M2 and substrate alignment marks PI, P2.

Referring to FIG. 1B, the radiation beam B is incident on the patterningdevice (for example, mask MA), which is held on the support structure(for example, mask table MT), and is patterned by the patterning device.Having traversed the mask MA, the radiation beam B passes through theprojection system PS, which focuses the beam onto a target portion C ofthe substrate W. The projection system has a pupil PPU conjugate to anillumination system pupil IPU. Portions of radiation emanate from theintensity distribution at the illumination system pupil IPU and traversea mask pattern without being affected by diffraction at a mask patterncreate an image of the intensity distribution at the illumination systempupil IPU.

With the aid of the second positioner PW and position sensor IF (forexample, an interferometric device, linear encoder, or capacitivesensor), the substrate table WT can be moved accurately (for example, soas to position different target portions C in the path of the radiationbeam B). Similarly, the first positioner PM and another position sensor(not shown in FIG. 1B) can be used to accurately position the mask MAwith respect to the path of the radiation beam B (for example, aftermechanical retrieval from a mask library or during a scan).

In general, movement of the mask table MT can be realized with the aidof a long-stroke module (coarse positioning) and a short-stroke module(fine positioning), which form part of the first positioner PM.Similarly, movement of the substrate table WT can be realized using along-stroke module and a short-stroke module, which form part of thesecond positioner PW. In the case of a stepper (as opposed to ascanner), the mask table MT can be connected to a short-stroke actuatoronly or can be fixed. Mask MA and substrate W can be aligned using maskalignment marks M1, M2, and substrate alignment marks PI, P2. Althoughthe substrate alignment marks (as illustrated) occupy dedicated targetportions, they can be located in spaces between target portions (knownas scribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the mask MA, the mask alignment marks can belocated between the dies.

Mask table MT and patterning device MA can be in a vacuum chamber, wherean in-vacuum robot IVR can be used to move patterning devices such as amask in and out of vacuum chamber. Alternatively, when mask table MT andpatterning device MA are outside of the vacuum chamber, an out-of-vacuumrobot can be used for various transportation operations, similar to thein-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots need tobe calibrated for a smooth transfer of any payload (e.g., mask) to afixed kinematic mount of a transfer station.

The lithographic apparatuses 100 and 100′ can be used in at least one ofthe following modes:

1. In step mode, the support structure (for example, mask table) MT andthe substrate table WT are kept essentially stationary, while an entirepattern imparted to the radiation beam B is projected onto a targetportion C at one time (i.e., a single static exposure). The substratetable WT is then shifted in the X and/or Y direction so that a differenttarget portion C can be exposed.

2. In scan mode, the support structure (for example, mask table) MT andthe substrate table WT are scanned synchronously while a patternimparted to the radiation beam B is projected onto a target portion C(i.e., a single dynamic exposure). The velocity and direction of thesubstrate table WT relative to the support structure (for example, masktable) MT can be determined by the (de-)magnification and image reversalcharacteristics of the projection system PS.

3. In another mode, the support structure (for example, mask table) MTis kept substantially stationary holding a programmable patterningdevice, and the substrate table WT is moved or scanned while a patternimparted to the radiation beam B is projected onto a target portion C. Apulsed radiation source SO can be employed and the programmablepatterning device is updated as required after each movement of thesubstrate table WT or in between successive radiation pulses during ascan. This mode of operation can be readily applied to masklesslithography that utilizes a programmable patterning device, such as aprogrammable mirror array of a type as referred to herein.

Combinations and/or variations on the described modes of use or entirelydifferent modes of use can also be employed.

Although specific reference can be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein can haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), and thin-filmmagnetic heads. The skilled artisan will appreciate that, in the contextof such alternative applications, any use of the terms “wafer” or “die”herein can be considered as synonymous with the more general terms“substrate” or “target portion,” respectively. The substrate referred toherein can be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool, and/or an inspectiontool. Where applicable, the disclosure herein can be applied to such andother substrate processing tools. Further, the substrate can beprocessed more than once, for example, in order to create a multi-layerIC, so that the term substrate used herein can also refer to a substratethat already contains one or multiple processed layers.

In a further embodiment, lithographic apparatus 100 includes an extremeultraviolet (EUV) source, which is configured to generate a beam of EUVradiation for EUV lithography. In general, the EUV source is configuredin a radiation system, and a corresponding illumination system isconfigured to condition the EUV radiation beam of the EUV source.

In the embodiments described herein, the terms “lens” and “lenselement,” where the context allows, can refer to any one or combinationof various types of optical components, including refractive,reflective, magnetic, electromagnetic, and electrostatic opticalcomponents.

Further, the terms “radiation” and “beam” used herein encompass alltypes of electromagnetic radiation, including ultraviolet (UV) radiation(for example, having a wavelength λ, of 365, 248, 193, 157 or 126 nm),extreme ultraviolet (EUV or soft X-ray) radiation (for example, having awavelength in the range of 5-20 nm such as, for example, 13.5 nm), orhard X-ray working at less than 5 nm, as well as particle beams, such asion beams or electron beams. Generally, radiation having wavelengthsbetween about 780-3000 nm (or larger) is considered IR radiation. UVrefers to radiation with wavelengths of approximately 100-400 nm. Withinlithography, the term “UV” also applies to the wavelengths that can beproduced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm;and/or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas),refers to radiation having a wavelength of approximately 100-200 nm.Deep UV (DUV) generally refers to radiation having wavelengths rangingfrom 126 nm to 428 nm, and in an embodiment, an excimer laser cangenerate DUV radiation used within a lithographic apparatus. It shouldbe appreciated that radiation having a wavelength in the range of, forexample, 5-20 nm relates to radiation with a certain wavelength band, ofwhich at least part is in the range of 5-20 nm.

Exemplary Embodiments of Patterning Device Supports Configured toControl the Temperature of a Patterning Device

FIGS. 2A and 2B illustrate a side view of a patterning device support200 that is configured to control the temperature of a patterning device202 according to embodiments. Patterning device support 200 can comprisea movable component 204, for example, a movable component of a reticlestage such as a short stroke module, that supports patterning device202. Radiation 206, such as the radiation beam B discussed in FIGS. 1Aand 1B above, is directed on patterning device 202. In some embodiments,patterning device 202 can be a reticle or other type of transmissivemask. As radiation 206 is incident on, and passes through, patterningdevice 202, patterning device 202 absorbs some energy from radiation206, which can cause a temperature increase and an associated thermalexpansion.

Patterning device support 200 may include one or more gas inlets 208 onone side of patterning device support 200. Gas inlet 208 can be integralwith movable component 204 as shown in FIG. 2A in some embodiments. Insome embodiments, gas inlet 208 can be separate from component 204, forexample, a separate nozzle that passes through an opening 205 defined bymovable component 204 as shown in FIG. 2B. Gas inlet 208 is adjacent toan end of patterning device 202. In some embodiments, movable component204 defines more than one opening 205 through which the nozzle may pass.

In some embodiments, gas inlet 208 is configured such that gas inlet 208moves with patterning device 202 during operational use of alithographic apparatus.

Movable component 204 may also include one or more gas outlets 210. Insome embodiments, gas outlet 210 can be integral with movable component204 as shown in FIG. 2A, or in some embodiments, gas outlet 210 can beseparate from component 204, for example, a separate nozzle that passesthrough an opening 207 defined by movable component 204 as shown in FIG.2B. Gas outlet 210 may be positioned at an opposing side of patterningdevice 202 relative to gas inlet 208. Gas outlet 210 may be adjacent anend of patterning device 202 opposite from the end of patterning device202 at which gas inlet 208 is adjacent. In some embodiments, gas outlet210 can be positioned at other suitable locations. Gas inlet 208 and gasoutlet 210 may each be situated so as to be in close proximity, forexample, adjacent to the same surface of patterning device 202, forexample, a top surface of patterning device 202.

Gas inlet 208 and gas outlet 210 are positioned and configured such thata gas flow 212 travels across a surface of patterning device 202. Insome embodiments, gas flow 212 travels from gas inlet 208 andsubstantially parallel to the surface of patterning device 202. Gasoutlet 210 extracts gas flow 212 as gas flow 212 reaches the oppositeside of patterning device 202. Extraction of gas flow 212 at gas outlet210 may be active or passive.

Gas flow 212 modifies the temperature of patterning device 202. Forexample, gas flow 212 can reduce, increase, or maintain the temperatureof patterning device 202. In some embodiments, gas flow 212 countersheating of patterning device 202 caused by radiation absorption, whichreduces the thermal expansion of patterning device 202 and heating ofthe gas around patterning device 202. This reduction in thermalexpansion of patterning device 202 and in the temperature of the gasaround patterning device 202 reduces the image distortion. In someembodiments, gas flow 212 maintains patterning device 202 at or near 20°C. at atmospheric pressure. Skilled artisans will appreciate that othertarget temperatures are possible and/or may be more desirable for agiven application. In some embodiments, one or more characteristics ofgas flow 212, for example, temperature, pressure, or flow rate, may bedynamically adjusted to achieve a desired temperature of patterningdevice 202. The desired temperature of patterning device 202 can bestatic or dynamic, and uniform or non-uniform. In some embodiments, thegas forming gas flow 212 comprises helium or consists essentially ofhelium. Helium may provide a 40-50% improvement in the cooling ofpatterning device 202 over other gases at the same velocity. Thisimprovement is due, in part, to helium having a thermal conductivitythat is about six times greater than conventional gas (0.026 for gas vs.0.148 for helium.) In some embodiments, gas flow 212 comprises anextremely clean dry gas or air. In some embodiments, gas flow 212 can betemporarily and selectively stopped while patterning device 202 isloaded on or unloaded from patterning device support 200 to avoiddisturbing the loading process. In some embodiments, gas flow 212 can betemporarily and selectively stopped when no cooling of patterning device202 is required. In some embodiments, the flow of gas flow 212 throughgas outlet 210 is stopped when the flow of gas flow 212 through gasinlet 208 is stopped. In some embodiments, the flow of gas flow 212 maybe stopped across the surface of the patterning device 202 when loadingor unloading the patterning device 202 on a movable component such asthe patterning device support 200 of a lithographic apparatus.

In some embodiments (not shown), gas inlet 208 and gas outlet 210 may bepositioned to cause gas flow 212 to flow across a bottom surface ofpatterning device 202.

In some embodiments (not shown), in addition to gas inlet 208 in closeproximity to the top surface of patterning device 202, an additional gasinlet may be integrated with patterning device support 200 in closeproximity to the bottom surface of patterning device 202, withcorresponding gas outlets in close proximity to the top and bottomsurfaces of patterning device 202. This configuration creates dualparallel flows of gas across the top and bottom surfaces of patterningdevice 202.

In some embodiments, patterning device 202 is a reflective patterningdevice, as discussed with respect to FIG. 1A above (not shown in FIG.2). Radiation beam 206 is still incident on patterning device 202 butwould be reflected from patterning device 202. In such circumstances,patterning device 202 may still be subject to heating and degradingeffects from the resulting thermal expansion of patterning device 202and the heating of the gas around patterning device 202. Patterningdevice support 200 may still comprise gas inlet 208 and gas outlet 210positioned within close proximity to a surface of patterning device 202,as discussed above.

In some embodiments, as explained below, gas flow 212 may be extractedby gas outlet 210 and recirculated back to gas inlet 208.

illustrates a top view of a patterning device support 300 according toan embodiment of the invention. Patterning device support 300 includessimilar components as the above described patterning device supports.These similar components are similarly numbered and are only describedto the extent they may differ or are helpful in explaining the disclosedembodiments. In FIG. 3, patterning device support 300 may include ashort stroke module 304 a and a long stroke module 304 b, as discussedabove with respect to FIGS. 1A and 1B. A gas inlet 308 may be integratedwith, or coupled to, long stroke module 304 b. Gas inlet 308 may includea gas supply nozzle 309, which is positioned proximate to a surface of apatterning device 302. A gas outlet 310 may be integrated with, orcoupled to, long stroke module 304 b at an opposing side of patterningdevice 302. Gas outlet 310 may include a gas extractor nozzle 311, whichis positioned proximate to the same surface of patterning device 302 asgas supply nozzle 309.

As depicted in FIG. 3, gas supply nozzle 309 and gas extractor nozzle311 are each approximately equal in length to the length of patterningdevice 302. In this configuration, a gas flow, such as gas flow 212 fromFIG. 2, can adequately reach approximately the entire surface ofpatterning device 202. Gas supply nozzle 309 and gas extractor nozzle311 may be longer, or shorter, than the length of patterning device 302.Gas supply nozzle 309 may be longer, shorter, or the same length as gasextractor nozzle 311.

Gas inlet 308 may extend through short stroke module 304 a via anopening 305 defined by short stroke module 304 a. Gas inlet 308 may beseparated from short stroke module 304 a. In a similar manner, gasoutlet 310 may extend through short stroke module 304 a via an opening307 defined by short stroke module 304 a. Gas outlet 310 may beseparated from short stroke module 304 a. Openings 305 and 307 may alsobe referred to as gaps, ports, or holes through a portion of shortstroke module 304 a. Openings 305 and 307 may be wide enough to allowshort stroke module 304 a to accurately position (such as movement alongline 356) patterning device 302 with respect to a substrate. The lengthof openings 305 and 307 may prevent gas inlet 308 or gas outlet 310 frominterfering with movement of short stroke module 304 a or contactingshort stroke module 304 a. As a result, any dynamic impact on shortstroke module 304 a from gas inlet 308 and gas outlet 310 withpatterning device support 300 may generally be minimized.

Additionally, dynamic impact of the gas flow across patterning device302 may be minimized because both nozzles 309 and 311 are substantiallystationary with respect to patterning device 302 (except for the finepositioning performed by short stroke module 304 a). The positioning ofgas supply nozzle 309 and gas extractor nozzle 311 may keep the gas flowfixed on patterning device 302 and minimizes any dynamic disturbances toeither patterning device 302 or patterning device support 300. Forexample, because gas supply nozzle 309 and gas extractor nozzle 311 mayboth move with long stroke module 304 b, there is minimal relativemotion of nozzles 309 and 311 with respect to patterning device 302 andpatterning device support 300. As a result, the gas flow from gas supplynozzle 309 may not cause a transient force on patterning device 302 asthe gas flow passes across a surface of patterning device 302. Further,because the gas flow is extracted by gas extractor nozzle 311 before thegas flow may reach a side of short stroke module 304 a, any net forceapplied to short stroke module 304 a may be minimized.

FIG. 4 illustrates a side view of a patterning device support 400according to an embodiment. Patterning device support 400 includessimilar components as the above described patterning device supports.These similar components are similarly numbered and are only describedto the extent they may differ or are helpful in explaining the disclosedembodiments. A gas inlet 408 and a gas outlet 410 may be integratedwith, or coupled to, a long stroke module 404 b. When integrated withlong stroke module 404 b, gas inlet 408 extends through one side of ashort stroke module 404 a via opening 405, and gas outlet 410 extendsthrough another, opposite side of short stroke module 404 a via opening407. This configuration may allow short stroke module 404 a toaccurately position a patterning device 402 with respect to a substratewithout causing gas inlet 408 or gas outlet 410 to interfere withmovement of short stroke module 404 a.

A gas supply nozzle 409 may be positioned proximate to a surface ofpatterning device 402 adjacent one end of patterning device 402 so as tocause a gas flow 412 across the surface toward a gas extractor nozzle411 of gas outlet 410. Gas extractor nozzle 411 may be positionedproximate to the same surface of patterning device 402 at the opposingend of patterning device 402 to extract gas flow 412. As gas flow 412passes across the surface of patterning device 402, gas flow 412 mayremove heat, for example, heat generated by a beam of radiation incidentupon patterning device 402, as discussed above with respect to FIGS. 2and 3. Gas flow 412 may change the temperature of patterning device 402or otherwise maintain a constant temperature of patterning device 402.

Nozzles 409 and 411 may have any suitable shape, size, or configuration.In some embodiments, nozzles 409 and 411 may each be a long tube with aplurality of holes substantially facing the surface of patterning device402 through which gas flow 412 may exit (nozzle 409) and enter (nozzle411). For example, the holes may be aimed at an angle that isnear-parallel but slightly tilted toward the surface of patterningdevice 402. In some embodiments, nozzles 409 and 411 may have aplurality of holes parallel to the surface of patterning device 402. Insome embodiments, nozzles 409 and 411 may each have a long tube with aplurality of individual nozzles facing the surface of patterning device402, which may more specifically direct and influence the manner inwhich gas flow 412 passes across the surface of patterning device 402.These nozzle configurations are exemplary only. A skilled artisan willappreciate that there are other nozzle configurations possible toprovide gas flow 412 across the surface of patterning device 402 withoutdeparting from the spirit and scope of the embodiments of the presentdisclosure.

Patterning device support 400 may also dynamically adjust thetemperature of patterning device 402 by changing differentcharacteristics of gas flow 412. In some embodiments, patterning devicesupport 400 includes one or more temperature sensors 419. Temperaturesensors 419 may be positioned at different locations and have differentconfigurations with respect to patterning device 402. For example,temperature sensors 419 may be attached to patterning device 402,integrated with short stroke module 404 b, or located a small distancefrom one or more locations of patterning device 402. A controller 420,for example, a processor, may be configured to receive signals fromtemperature sensors 419 that indicate the temperature at one or morelocations of patterning device 402. Temperature sensor(s) 419 may bepositioned and configured to sense a temperature at a location withinthe system, for example, the temperature of patterning device 402, thetemperature of gas flow 412 entering the environment containingpattering device 402, the temperature of gas flow 412 exiting theenvironment containing patterning device 402, the temperature of the gasin the environment containing patterning device 402, or any combinationof these temperatures.

Controller 420 may be configured to communicate with a coolingsub-system (not shown). In some embodiments, controller 420 dynamicallyadjusts the temperature of patterning device 402 by varying one or morecharacteristics of gas flow 412, for example, temperature, pressure, orflow rate of gas flow 412 to achieve a desired temperature of patterningdevice 402. The desired temperature of patterning device 402 can bestatic or dynamic, and uniform or non-uniform. Controller 420 may varythe flow rate of gas flow 412 at a plurality of exits in gas supplynozzle 409, depending on the configuration of nozzle 409 as discussedabove.

In some embodiments, gas supply nozzle 409 may additionally include atemperature control element, for example, a heat exchanger, that isconfigured to change the temperature of gas flow 412 as it exits gassupply nozzle 409. This temperature control element may be, for example,one or more heaters attached to or integrated with gas supply nozzle409. This temperature control element may be located at other locations,for example, at locations upstream of gas supply nozzle 409. Controller420 may additionally dynamically adjust the temperature of gas flow 412by a different amount at a plurality of exits in gas supply nozzle 409,depending on the configuration of nozzle 409 as discussed above.

Additionally, patterning device support 400 may control the temperatureof patterning device 402 by a combination of varying the flow rate ofgas flow 412 and a temperature of gas flow 412. In some embodiments,controller 420 may also be configured to adjust one or morecharacteristics of gas flow 412 based on the status of the lithographicapparatus. For example, controller 420 may decrease the velocity and/orvolume of gas flow 412 when the system is not imaging a substrate, andincrease the velocity and/or volume of gas flow 412 when the system isimaging a substrate. The skilled artisan will recognize that othervariations of control are also possible that fall within the scope ofthe embodiments of the present disclosure.

FIGS. 5A and 5B illustrate a side view of a patterning device support500 that is configured to control the temperature of a patterning device502, and a fixed component 503 of a lithographic apparatus according toembodiments. Patterning device support 500 includes similar componentsas the above described patterning device supports. These similarcomponents are similarly numbered and are only described to the extentthey may differ or are helpful in explaining the disclosed embodiments.Patterning device support 500 may comprise a movable component 504, forexample, a movable component of a reticle stage, that supportspatterning device 502. Radiation 506, such as the radiation beam Bdiscussed in FIGS. 1A and 1B above, is directed on patterning device502. In some embodiments, patterning device 502 can be a reticle orother type of transmissive mask. As radiation 506 is incident on, andpasses through, patterning device 502, patterning device 502 absorbssome energy from radiation 506, which can cause a temperature increaseand an associated thermal expansion, as well as a heating of the gasaround patterning device 502. In some embodiments, component 503 is anon-movable component of a lithographic apparatus, for example, a fixedpurge plate. Fixed purge plate 503 may be, for example, about 1.5 mmabove patterning device support 500. Fixed purge plate 503 may define,in part, a pressurized environment that contains clean gas in the areabetween patterning device 502 and a bottom surface of fixed purge plate503. Gas outlet 510 may be positioned, for example, at an opening orport along a long axis of the scanning stage in plate 503. The long axisof the scanning stage may be along the direction of the movement 356shown in FIG. 3, for example. In some embodiments, gas outlet 510 mayextend to cover the full range of movement possible along the long axisof the scanning stage. In some embodiments which gas outlet 510 ispositioned at fixed purge plate 503, gas outlet 510 remains stationaryduring operational use of the lithographic apparatus.

Patterning device support 500 may include a gas inlet 508. In someembodiments, gas inlet 508 may be integral with movable component 504 asshown in FIG. 5A. For example, movable component 504 may form or bedirectly coupled to a nozzle. In some embodiments, gas inlet 508 may beseparate from component 504, for example, a separate nozzle that passesthrough an opening 505 defined by movable component 504 as shown in FIG.5B. Component 503 may include a gas outlet 510. As shown in FIGS. 5A and5B, gas outlet 510 may be integrated with or coupled to fixed purgeplate 503 that is above patterning device 502. Gas outlet 510 may bepositioned at an opposing side of patterning device 502 relative to gasinlet 508. Gas inlet 508 and gas outlet 510 may each be situated so asto be in close proximity, for example, adjacent to the same surface ofpatterning device 502, for example, a top side of patterning device 502.

Gas inlet 508 and gas outlet 510 are positioned to provide a gas flow512 across a surface of patterning device 502. In FIGS. 5A and 5B, gasflow 512 travels from gas inlet 508 and across and substantiallyparallel to the top surface of patterning device 502. Gas outlet 510extracts gas flow 512 as gas flow 512 reaches the opposite side ofpatterning device 502.

Gas flow 512 modifies the temperature of patterning device 502. Forexample, gas flow 512 can reduce, increase, or maintain the temperatureof patterning device 502. In some embodiments, gas flow 512 countersheating of patterning device 202 caused by radiation absorption, whichreduces the thermal expansion of patterning device 202 and heating ofthe gas around patterning device 202. This reduction in thermalexpansion of patterning device 202 and in the temperature of the gasaround patterning device 202 reduces the image distortion. In someembodiments, the characteristics of gas flow 512, for example,temperature, pressure, or flow rate, may be dynamically adjusted toachieve a desired temperature of patterning device 502. The desiredtemperature of patterning device 502 can be static or dynamic, anduniform or non-uniform. In some embodiments, the gas of gas flow 512comprises helium or consists essentially of helium. In some embodiments,gas flow 512 comprises an extremely clean dry gas or air.

Gas flow 512 extracted by gas outlet 510 can be recirculated back to gasinlet 508 as discussed below.

FIG. 6 is a schematic illustration of an exemplary infrastructureaccording to an embodiment. In FIG. 6, a gas supply 601 supplies a gas.Gas supply 601 may supply, for example, extremely clean dry gas or air.In some embodiments, the gas from supply 601 may flow at a rate of about20 normal liters per second. A skilled artisan will recognize that othergas flow rates and other gases are possible without departing from thescope of the present disclosure.

The infrastructure may also include a supply inflow duct 603 thattransports the gas from supply 601 to one or more supply hoses 616 to apatterning device support of a lithographic apparatus. Supply hoses 616may include, for example, five hoses of equal or varying diameter. Insome embodiments, each supply hose 616 may have an inner diameter ofabout 10 mm. In some embodiments, the diameter of each supply hose 616may be sized to create an overpressure, for example, an overpressure ofseveral bars. In some embodiments, a restrictive member of a nozzle maycreate an overpressure. The overpressure may lower the velocity andcreate a good flow layer across a patterning device. Supply hoses 616may be of any material, for example, polytetrafluoroethylene, that isclean or very clean and emits minimal molecular contamination, forexample, outgassing, to the gas flow provided from supply 601. In someembodiments, supply hoses 616 may be made of polyurethane. Skilledartisans will recognize that other materials and diameters may also beused, as well as more or fewer hoses than five to bring the gas flow toone or more supply nozzles. Supply hoses 616 may be integrated with asystem configured to bring water and gas to the patterning devicesupport.

Supply hoses 616 may be connected to a gas inlet 608 at a movablecomponent of the patterning device support. Gas inlet 608 may includeone or more nozzles as discussed above. The gas from supply 601 isemitted from gas inlet 608 and flows across a surface of the patterningdevice as gas flow 612. In some embodiments, the surface of thepatterning device is a top surface of a patterning device. In someembodiments, gas inlet 608 is tilted to direct gas flow 612 toward thesurface of the patterning device and, in some embodiments, toward thecenter of the patterning device. Gas flow 612 may cool or otherwisemaintain a constant temperature of the patterning device.

After gas flow 612 crosses the surface of the patterning device, a gasoutlet 610 extracts gas flow 612. In some embodiments, gas outlet 610 iscoupled to or integrated with a gas extraction slot in a fixed purgeplate at an end of the patterning device opposite gas inlet 608, asdiscussed above with respect to FIGS. 5A and 5B. Gas outlet 610 mayextend along a long axis of the patterning device support. Theinfrastructure may also include a fan 613 that facilitates extraction ofgas flow 612.

After gas flow 612 is extracted at gas outlet 610, gas flow 612 may passthrough an extraction hose 614. Extraction hose 614 may be, for example,about 50 mm in diameter. The diameter of extraction hose 614 can besized to achieve a desired specific gas flow rate, for example, a gasflow rate of about 20 normal liters per second. The diameter ofextraction hose 614 can also be sized to maintain the dynamics of gasflow 612 after extraction. Other diameters and flow rates are possible,as will be recognized by those skilled in the relevant arts. Positioninggas outlet 610 in a fixed purge plate, in contrast to being integratedwith or coupled to a movable component of the pattering device support,may be advantageous in situations in which extraction hose 614 is of asignificant diameter, for example, about 50 mm, which makes it difficultto extend extraction hose 614 close to the reticle stage as would benecessary for integrating or coupling to the long stroke module.

Fan 613 may be an existing fan already utilized in other aspects of thelithographic system or an additional, separate fan system, as will berecognized by those skilled in the relevant arts. In some embodiments,fan 613 creates a pressure difference that causes a flow from gas outlet610 toward fan 613, for example, in a direction away from the surface ofthe patterning device.

FIGS. 21 and 22 are schematic illustrations of exemplary closed-loopcontrol infrastructures according to embodiments. The infrastructures ofFIGS. 21 and 22 include similar components as the above describedinfrastructure of FIG. 6. These similar components are similarlynumbered and are only described to the extent they may differ. As shownin FIG. 21, a temperature control element 2130, for example, a heatexchanger, is operatively coupled between gas supply 2101 and gas inlet2108. Temperature control element 2130 is configured to adjusttemperature of gas supplied from gas supply 2101. A temperature sensor2119 configured to determine a temperature of the gas may be positioneddownstream from gas outlet 2110. The infrastructure can include acontroller 2120 operatively coupled to temperature sensor 2119 and totemperature control element 2130. Controller 2120 is configured toreceive a signal from temperature sensor 2119 and, based on the receivedsignal, controller 2120 communicates with heat exchanger 2130 to adjustthe temperature of gas flow being supplied by gas supply 2101. In FIG.22, a temperature sensor 2219 is positioned between a gas inlet 2208 anda gas outlet 2210.

Although only one sensor 2119 and sensor 2219 is shown in FIGS. 21 and22, more than one sensor 2119 and sensor 2219 may be used. Controllers2120 and 2220 may also process other signals in addition to thesignal(s) received from temperature sensors 2119 and 2219. For example,controllers 2120 and 2220 may process the expected amount of dose usedduring exposure of patterning devices 2102 and 2202, and controllers2120 and 2220 may vary one or more characteristics of gas flows 2112 and2213 based on the expected dose, for example, to optimize the controlloop used during a feed forward mode.

In some embodiments (not shown), temperature sensors 2119 and 2219 arepositioned in a nozzle at gas inlets 2108 and 2208. In such embodiments,the Joule-Thomson effect could be compensated for knowing the pressurein the nozzle, for example, by using a pressure sensor in the nozzle orby design or calibration.

Temperature sensors 2119 and 2219 may be positioned at other suitablelocations, for example, at inlets 2108 and 2208, at outlets 2110 and2210, or upstream of inlets 2108 and 2208.

FIG. 7A illustrates a patterning device support 700 according to anembodiment. Patterning device support 700 includes similar components asthe above described patterning device supports. These similar componentsare similarly numbered and are only described to the extent they maydiffer or are helpful in explaining the disclosed embodiments. A movablecomponent 704 of patterning device support 700, for example, a shortstroke module, can define a first channel 732 on one side of apatterning device 702, and a second channel 734 on an opposing side ofpatterning device 702. As shown in FIG. 7A, this temperature controlsystem does not require a gas supply. Rather, the temperature of asurface, for example, a top or bottom surface, of a patterning device702 is controlled by generating a flow of gas through channel 732,across a surface of patterning device 702, and then through channel 734.Channels 732 and 734 may extend entirely through movable component 704in some embodiments. Channels 732 and 734 may be positioned at oppositeends of moveable component 704 or substantially around an entireperimeter of moveable component 704. Moveable component 704 may be ashort stroke module or a long stroke module in some embodiments. In someembodiments, channels 732 and 734 extend through both a long strokemodule and a short stroke module. Movable component 704 may scan alongan axis.

Patterning device 702 may rest upon patterning device support 700. Asmoveable component 704 moves, ambient gas around support 700 is forcedthrough a leading channel, for example, channel 732 or channel 734. Theshape and orientation of channels 732 and 734 may be designed so thatgas flows substantially parallel across a surface of patterning device702 as illustrated in FIG. 7A. For example, channels 732 and 734 mayhave a tapered geometry to direct the gas or include curved surfaces toaid in funneling the gas across the surface of patterning device 702. Inone embodiment, channels 732 and 734 may be present both above and belowpatterning device 702 to direct gas substantially parallel and acrossboth a top and bottom surface of patterning device 702. In someembodiments, channels 732 and 734 may only be present below patterningdevice 702 to direct gas substantially parallel and across the bottomsurface of patterning device 702. The movement of gas across thesurface(s) of patterning device 702 may control the temperature ofpatterning device 702. For example, flowing gas that is colder thanpatterning device 702 will lower the temperature of patterning device702.

The lithographic apparatus may also include a plate 703 positioned abovepatterning device 702. Plate 703 may enclose, in part, an area betweenplate 703 and patterning device 702 to maintain the temperature ofpattering device 702 and contain the gas flow in some embodiments. Plate703 may be, for example, about 1.5 mm above the scanning stage ofpatterning device support 700. Plate 703 may include an opening to allowa beam of radiation 706 to impinge upon the surface of patterning device702. Beam of radiation 706 may exit from an optical element 711, forexample, a component of the illumination optics in a lithographicapparatus.

FIG. 7B illustrates an enlarged view of a channel 732 or 734 extendingthrough movable component 704. An end of patterning device 702 isillustrated resting upon a surface of movable component 704. In someembodiments, a temperature control element 710, for example, a heatexchanger, is positioned within channel 732. Temperature control element710 may control the temperature of the gas moving through channel 732.For example, temperature control element 710 may cool the gas before itflows across the surface of patterning device 702.

In some embodiments, temperature control element 710 may use roughcooling water (RCW) to cool the gas. The RCW may already be in use forcooling motors that control, for example, moveable component 704. Thus,the same RCW system being used for cooling other parts of patterningdevice support 700 may be used for cooling the gas within channel 732 aswell. In some embodiments, the RCW system is designed such that the gaswithin channel 732 is cooled by the water before the water is used tocool other components, for example, the motors that control movablecomponent 704.

In some embodiments, temperature control element 710 is a thermoelectriccooling device. For example, the thermoelectric cooling device can be aPeltier device that cools gas on one side of the device by an appliedcurrent. The current may be adjusted to control the temperature of thegas moving through channel 732. The heat transfer within channel 732 maybe doubled or tripled depending on whether temperature control element710 is used.

FIG. 8 illustrates a patterning device support 800 according to anembodiment. Patterning device support 800 includes similar components asthe above described patterning device supports. These similar componentsare similarly numbered and are only described to the extent they maydiffer or are helpful in explaining the disclosed embodiments. A movablecomponent 804 a of patterning device support 800, for example, a shortstroke module, can define a first channel 832 on one side of apatterning device 802, and a second channel 834 on an opposing side ofpatterning device 802, as described above with reference to FIGS. 7A and7B. As shown in FIG. 8, the temperature control system may also use agas inlet 808 and a gas outlet 810 as described above with reference toFIG. 4. Gas flow 812 across the surface of patterning device 802 isgenerated by a combination of gas supplied by gas inlet 808 and gaspassing through channel 832 generated by movement of movable component804 a.

Exemplary Embodiments of Methods of Controlling the Temperature of aPatterning Device

FIG. 9 is a flow diagram of a method 900 for controlling the temperatureof a patterning device according to an embodiment. It is to beappreciated that operations in method 900 may be performed in anotherorder, and that not all operations shown may be needed. Method 900starts at step 901 when, for example, the patterning device isilluminated with a radiation beam. The patterning device may be, forexample, a reticle. At step 903, a gas flow is supplied across a surfaceof the patterning device. In some embodiments, the gas flow issubstantially parallel to a surface, for example, a top surface, of thepatterning device. In some embodiments, the gas flows across a bottomsurface of the patterning device. In some embodiments, the gas flow isintroduced by a gas inlet, for example, as discussed above with respectto FIGS. 2-6 and 8, or by a channel defined by a movable component asdiscussed above with respect to FIGS. 7A, 7B, and 8.

At step 905, the gas flow modifies or maintains the temperature of thepatterning device, for example, because the gas flow is at a lowertemperature. A characteristic of the gas flow, for example, thevelocity, volume, and/or temperature, can be adjusted to variably affectthe temperature of the patterning device, as will be recognized by theskilled artisan. In some embodiments, the channeled gas includes helium.

At step 907, the gas flow is extracted from the surface of thepatterning device at an opposite end of the patterning device. In someembodiments, the gas flow is extracted by a gas outlet, for example, asdiscussed above with respect to FIGS. 2-6, or by a channel defined by amovable component as discussed above with respect to FIGS. 7A, 7B, and8.

In some embodiments, the gas flow is continually supplied while thelithographic apparatus is in operation. In some embodiments, the gasflow is continually supplied while the lithographic apparatus is inoperation such that the temperature of the patterning device isconstantly maintained. In some embodiments, the temperature of thepatterning device is maintained at or about a target temperature, forexample, about 22° C.

FIG. 10 is a flow diagram of a method 1000 for controlling thetemperature of a patterning device according to an embodiment. It is tobe appreciated that operations in method 1000 may be performed inanother order, and that not all operations shown may be needed. As shownin FIG. 10, method 1000 may begin at step 1002 by moving a moveablecomponent that is coupled to a patterning device. The patterning devicemay rest upon a surface of the moveable component that is eitherattached to or part of the movable component. The movable component maymove along an axis, for example, during a scanning motion.

Method 1000 continues with step 1004 at which gas is pushed through oneor more channels by movement of the movable component as shown in FIGS.7A-7B. The one or more channels may extend through the moveablecomponent. The one or more channels may be positioned on opposite sidesof the movable component along a first axis such that gas is pushedthrough the channels on the opposite sides when the moveable body movesalong the first axis. For example, gas may be pushed through thechannels on one side of the moveable component when the moveablecomponent moves in a first direction along the first axis, and the gasmay be pushed through the channels on the opposite side of the moveablecomponent when the moveable body moves in the opposite direction fromthe first direction. The channeled gas may further be cooled via atemperature control element, such as, for example, an RCW system orthermoelectric cooling device.

At step 1006, the channeled gas flows across a surface of the patterningdevice. In some embodiments, the gas flow is substantially parallel tothe surface of the patterning device. The flowing of the gas may cause atemperature change in the patterning device, for example, a drop in thetemperature of the patterning device. In some embodiments, the channeledgas includes helium.

Exemplary Embodiments of Patterning Device Supports that Recirculate theGas Flow

FIG. 11 illustrates a top view of a patterning device support 1100configured to control the temperature of a patterning device 1102according to an embodiment. Patterning device support 1100 includessimilar components as the above described patterning device supports.These similar components are similarly numbered and are only describedto the extent they may differ or are helpful in explaining the disclosedembodiments. Patterning device support 1100 can comprise a first movablecomponent 1104 a and a second movable component 1104 b, for example, theshort-stroke module and the long-stroke module as discussed above withrespect to FIGS. 1A and 1B. Patterning device support 1100 can comprisea gas inlet 1108 positioned proximate to a surface of patterning device1102. Patterning device support 1100 can also include gas outlet 1110positioned proximate to the same surface of patterning device 1102 asgas inlet 1108. In some embodiments, gas inlet 1108, gas outlet 1110,first movable component 1104 a, and second movable component 1104 b canbe configured as described in U.S. Provisional Patent Application Nos.61/768,125, filed Feb. 22, 2013; 61/752,751, filed Jan. 15, 2013; and61/720,628, filed Oct. 31, 2012, which are incorporated herein in theirentireties by reference. In some embodiments, patterning device support1100 can be configured as described in U.S. Provisional PatentApplication Nos. 61/824,695, filed May 17, 2013; and 61/767,060, filedFeb. 20, 2013, which are incorporated herein in their entireties byreference. In some embodiments, patterning device support 1100 can beconfigured as described in U.S. Provisional Patent Application No.61/767,184, filed Feb. 20, 2013, which is incorporated herein in itsentirety by reference.

As depicted in FIG. 11, gas inlet 1108 and gas outlet 1110 areelongated, and each is approximately equal in length to the length ofpatterning device 1102 in some embodiments. In such embodiments, gasflow 1112 is able to adequately flow over substantially the entirelysurface of patterning device 1102. As will be recognized by the skilledartisan, gas inlet 1108 and gas outlet 1110 can be longer or shorterthan the length of patterning device 1102 without departing from thegeneral concept of the present invention. Gas inlet 1108 and gas outlet1110 can assume various shapes, sizes, types, and configurations. Insome embodiments, gas inlet 1108 and gas outlet can each comprise anozzle that is either integral with or separate from movable component1104 a. In some embodiments, the nozzle of gas outlet 1110 can be largerthan the nozzle at gas inlet 1108.

As shown in FIG. 11, gas flow 1112 extracted through gas outlet 1110 isrecirculated from gas outlet 1110 to gas inlet 1108. For example, gasflow 1112 passes through gas inlet 1108 and travels across the surfaceof patterning device 1102 toward gas outlet 1110. Gas outlet 1110extracts gas flow 1112. At least one duct defines a recirculation pathfrom gas outlet 1110 to gas inlet 1108. At that point, gas flow 1112again passes through gas inlet 1108 and across patterning device 1102 ina continuous cycle.

In some embodiments, movable component 1104 b comprises at least aportion of the recirculatory path. For example, as shown in FIG. 11, therecirculatory path includes an outlet duct 1114, an inlet duct 1116, anda gas flow generator 1118 spaced between the outlet duct 1114 and theinlet duct 1116. Outlet duct 1114, inlet duct 1116, and gas flowgenerator 1118 are positioned on movable component 1104 b, for example,the long-stroke module.

In some embodiments, outlet duct 1114, inlet duct 1116, and gas flowgenerator 1118 are positioned on movable component 1104 a, for example,the short-stroke module. For example, gas flow generator 1118 can beadjacent to gas inlet 1108 on movable component 1104 a. And in someembodiments, at least one of outlet duct 1114, inlet duct 1116, and gasflow generator 1118 is positioned on movable component 1104 b and atleast one is positioned on movable component 1104 a.

Gas flow generator 1118 can be any suitable device that causes the gasto flow for recirculation. For example, gas flow generator 1118 can be agas amplifier (as discussed, for example, below with reference to FIG.13) a pump, a fan, or any other suitable device that moves a gas.

In some embodiments in which gas flow generator 1118 is a pump, the pumpis driven by one or more fans positioned on patterning device support1100 (as discussed below with reference to FIG. 17). For example, thescanning motion of patterning device support 1100 can create an externalgas flow that drives the fans which in turn drives the pump.

In some embodiments in which gas flow generator 1118 is a pump, the pumpis driven by a piston. For example, the scanning motion of patterningdevice support 1100 can create inertia that causes the piston to movewithin the chamber and, in turn, drives the pump.

In some embodiments, recirculating gas flow 1112 has one or more of thefollowing advantages over a non-recirculating gas flow: (1)recirculation reduces the amount of gas consumption, which in turndecreases the cost of ownership, decreases the supply infrastructurerequirements, simplifies the duct work (which can help packaging andreliability), and decreases the required infrastructure within thelithographic apparatus to supply and extract the required volume of gas;(2) recirculation minimizes any required modifications to theilluminator to achieve the required volume for the microenvironmentdefined by patterning device support 1100 above patterning device 1102if, for example, a fixed plate comprises the gas outlet; and (3)recirculation easily allows for gas flow extraction on patterning devicesupport 1100 which in turn enables extraction closer to a surface ofpatterning device 1102, and provides a more uniform extraction comparedto the long extraction duct required when extraction is on a fixedcomponents, for example, the fixed purge plate.

In some embodiments, the microenvironment defined by patterning devicesupport 1100 above patterning device 1102 is not completely sealed. Forexample, there can be an air gap between the patterning device support1100 and a fixed purge plate (not shown in FIG. 11). This air gap canprovide a leakage path for excess gas flow to escape. In someembodiments, an overpressure is created in the microenvironment abovepatterning device 1102 such that excess gas flow escaping through theair gap prevents non-conditioned gas from reaching the microenvironment.The small leakage flow can help ensure that the recirculated gas flow1112 remains properly clean and dry.

In some embodiments, outlet duct 1114 or inlet duct 1116 comprises atleast one opening that provides a leakage path for excess gas flow toescape or additional gas to be drawn in. In some embodiments, theopening in outlet duct 1114 or inflow duct 1116 is sealed with anadjustable valve. The adjustable valve can be opened when a pressuresensor (not shown) senses a predetermined pressure in outlet duct 1114or inlet duct 1116.

In some embodiments, a gas leaked from the system can be routed to purgethe elements of the projection lens and/or the illuminator, or to coolmotor coils and magnets of the lithographic apparatus.

As gas flow 1112 passes across the surface of patterning device 1102,gas flow 1112 may modify the temperature of patterning device 1102. Forexample, gas flow 1112 can remove heat generated by radiation incidentupon patterning device 1102, for example, as discussed above withrespect to FIGS. 2A, 2B, 5A, and 5B. So gas flow 1112 can coolpatterning device 1102 or otherwise maintain a constant temperature ofpatterning device 1102.

In some embodiments, outlet duct 1114 and inlet duct 1116 can eachcomprise one or more hoses made of any material that is clean or veryclean and emits minimal molecular contamination (for example,outgassing) to the gas flow.

In some embodiments, gas flow 1112 comprises an extremely clean dry gasor air.

In some embodiments, the lithographic apparatus can include a controller

1120, for example, a processor, configured to adjust one or morecharacteristics of gas flow 1112, for example, temperature, flow rate,pressure, or velocity, to maintain, decrease, and/or increase thetemperature of patterning device 1102. For example, controller 1120 canbe operatively coupled with a temperature control element, for example,a heat exchanger, to adjust temperature of gas flow 1112, a flow controlvalve to adjust the pressure or flow rate of gas flow 1112, or air flowgenerator 1118 to control the flow rate.

In some embodiments, controller 1120 is configured for closed-loopcontrol.

For example, in some embodiments, controller 1120 is configured toreceive signals from one or more sensors configured to measure acharacteristic of gas flow 1112, for example, one or more temperaturesensors, one or more pressure sensors, and/or one or more flow sensors.Based on the received signal(s), controller 1120 can adjust one or morecharacteristics of gas flow 1112 to achieve a desired temperature ofpatterning device 1102. For example, controller 1120 can be configuredto communicate with a temperature control element (not shown in FIG.11), for example, a heat exchanger, to adjust the temperature of gasflow 1112, or communicate with gas flow generator 1118 to adjust theflow rate of gas flow 1112. In some embodiments, controller 1120 isconfigured to process other signals, for example, signals from othercomponents of the system related to the expected dose used duringexposure.

For example, as shown in FIG. 11, patterning device support 1100comprises a temperature sensor 1119 operatively coupled with controller1120. Temperature sensor 1119 may be configured to sense a temperatureat location within the system. For example, temperature sensor 1119 maybe configured to measure the temperature of patterning device 1102, thetemperature of gas flow 1112 entering the environment containingpattering device 1102, the temperature of gas flow 1112 exiting theenvironment containing patterning device 1102, the temperature of thegas in the environment containing patterning device 1102, or anycombination of these temperatures. For example, as shown in FIG. 11,temperature sensor 1119 can be positioned downstream of gas inlet 1108in gas flow 1112 to measure the temperature of gas flow 1112 enteringthe environment containing pattering device 1102. In embodiments inwhich gas inlet 1108 or gas outlet 1110 are thermally conductive, sensor1119 can be positioned on gas inlet 1108 or gas outlet 1110.

In some embodiments, controller 1120 can be configured to adjust one ormore characteristics of gas flow 1112 based on the status of thelithographic apparatus. For example, controller 1120 can decrease thevolume or velocity of gas flow 1112 and/or increase the temperature ofgas flow 1112 when the lithographic apparatus is not imaging asubstrate, and increase the volume or velocity of gas flow 1112 ordecrease the temperature of gas flow 1112 when the system is imaging asubstrate.

The skilled artisan will recognize that other variations of control arealso possible that fall within the scope of the present disclosure.

FIG. 12 illustrates a top view of a patterning device support 1200configured to control the temperature of a patterning device 1202according to an embodiment. Patterning device support 1200 includessimilar components as the above described patterning device supports,which are similarly numbered and are only described to the extent thesecomponents may differ or are helpful in explaining the disclosedembodiments. Patterning device support 1200 includes a temperaturesensor 1219 and a pressure sensor 1221 positioned upstream of a gasinlet 1208. Temperature sensor 1219 and pressure sensor 1221 areoperatively coupled to a controller 1220. Controller 1220 uses thesignals received from temperature sensor 1219 and pressure sensor 1221to estimate the temperature of gas flow 1212 at a location downstream ofgas inlet 1208, for example, at a location proximate to a patterningdevice 1202.

Referring to FIGS. 11 and 12, temperature sensors 1119 and 1219 andpressure sensor 1221 may be attached to patterning device 1102 or 1202,or coupled to patterning device support 1100 or 1200 (for example, onmovable component 1104 a or 1204 a or movable component 1104 b or 1204b).

In some embodiments, controller 420 can be configured control thetemperature of patterning device 402 without closed loop feedback, forexample, by using calibration or a feed forward configuration.

FIG. 13 illustrates a top view of a patterning device support 1300configured to control the temperature of a patterning device 1302according to an embodiment in which the gas flow generator 1318 is a gasamplifier. Patterning device support 1300 includes similar components asthe above described patterning device supports, which are similarlynumbered and are only described to the extent these components maydiffer or are helpful in explaining the disclosed embodiments. Gasamplifier 1318 uses a high velocity stream of supply gas 1320 to movethe gas flow from inlet duct 1316 to the outlet duct 1314. In someembodiments, gas amplifier 1318 can amplify the total gas flow volume byabout 2 to 50 tens of times the volume of the incoming flow of supplygas 1320.

In some embodiments, one or more characteristics of supply gas 1320 canbe adjusted to control the temperature of gas flow 1312 over thereticle. For example, a temperature control element, such as a heatexchanger, can be operatively coupled to supply gas as shown in FIG. 14.

FIG. 14 illustrates a top view of a patterning device support 1400configured to control the temperature of a patterning device 1402according to an embodiment. Patterning device support 1400 includessimilar components as the above described patterning device supports.These similar components are similarly numbered and are only describedto the extent they may differ or are helpful in explaining the disclosedembodiments. As shown in FIG. 14, the lithographic apparatus comprises atemperature control element 1430 configured to adjust a temperature ofsupply gas 1420 of gas amplifier 1418. Temperature control element 1430can be any suitable device that changes the temperature of a gas flow.In some embodiments, a controller 1420 is operatively coupled withtemperature control element 1430 to dynamically control the temperatureof supply gas 1420 and, in turn, gas flow 1412 and then of patterningdevice 1402.

In some embodiments, one or more characteristics of the gas flow can beadjusted within the recirculatory ducts to control the temperature ofthe patterning device. For example, a temperature control element can beoperatively coupled to a recirculatory duct to adjust the temperature ofthe gas flow.

FIG. 15 illustrates a top view of a patterning device support 1500configured to control the temperature of a patterning device 1502according to an embodiment. Patterning device support 1500 includessimilar components as the above described patterning device supports.These similar components are similarly numbered and are only describedto the extent they may differ or are helpful in explaining the disclosedembodiments. As shown in FIG. 15, patterning device support 1500includes a temperature control element 1530 configured to change atemperature of the gas in the recirculatory path. For example,temperature control element 1530 can be positioned at the inlet duct1516 downstream from gas flow generator 1518 as shown in FIG. 15. Insome embodiments, a controller 1520 is operatively coupled totemperature control element 1530 to dynamically change the temperatureof the gas in the recirculatory path. FIG. 16 illustrates a top view ofa patterning device support 1600 configured to control the temperatureof a patterning device 1602 according to another embodiment. Patterningdevice support 1600 includes similar components as the above describedpatterning device supports. These similar components are similarlynumbered and are only described to the extent they may differ or arehelpful in explaining the disclosed embodiments. As shown in FIG. 16, atemperature control element 1630 can be positioned upstream from an gasflow generator 1618.

FIG. 17 illustrates a top view of a patterning device support 1700configured to control the temperature of a patterning device 1702according to an embodiment in which the gas flow generator comprises apump 1718. Patterning device support 1700 includes similar components asthe above described patterning device supports. These similar componentsare similarly numbered and are only described to the extent thecomponents may differ or are helpful in explaining the disclosedembodiments. A fan 1733 drives pump 1718. Fan 1733 is driven by theexternal gas flow caused by the scanning motion of patterning devicesupport 1700.

FIG. 18 illustrates a top view of a patterning device support 1800configured to control the temperature of a patterning device 1802according to an embodiment. Patterning device support 1800 includessimilar components as the above described patterning device supports.These similar components are similarly numbered and are only describedto the extent they may differ or are helpful in explaining the disclosedembodiments.

In some embodiments, an outlet duct 1814 can include a first branch 1822and a second branch 1824. First branch 1822 can direct a portion of gasflow 1812 from gas outlet 1810 to a first gas flow generator 1818 a.Second branch 1824 can direct a portion of gas flow 1812 from gas outlet1810 to a second gas flow generator 1818 b. First gas flow generator1818 a can be positioned on a side of patterning device 1802 that isopposite from second gas flow generator 1818 b.

In some embodiments, an inlet duct 1816 can include a first branch 1826and an opposing second branch 1828. First branch 1826 can direct gasflow 1812 from first gas flow generator 1818 a to gas inlet 1808. Secondbranch 1828 can direct gas flow 1812 from second gas flow generator 1818b to gas inlet 1808.

FIG. 19 illustrates a side view of a patterning device support 1900 thatis configured to control the temperature of a patterning device 1902according to an embodiment. Patterning device support 1900 includessimilar components as the above described patterning device supports.These similar components are similarly numbered and are only describedto the extent they may differ or are helpful in explaining the disclosedembodiments. As shown in FIG. 19, patterning device support 1900 can beconfigured such that a gas flow 1912 recirculates within amicroenvironment 1931 containing patterning device 1902. Patterningdevice support 1900 includes a gas amplifier 1918 positioned withinenvironment 1931. Gas amplifier 1918 can use a high velocity stream ofsupply gas 1920 to push gas flow 1912 from a gas inlet 1908 inenvironment 1931. After exiting gas inlet 1908, gas flow 1912 travelsacross a surface of patterning device 1902. Movable component 1904 isshaped such that after gas flow 1912 travels across patterning device1902 it is redirected back towards a gas outlet 1910 entirely withinenvironment 1931. Gas amplifier 1918 can define gas outlet 1910 or canbe operatively coupled to gas outlet 1910. One advantage of locallyrecycling gas flow 1912 within microenvironment 1931 is that externalconnections through movable component 1904 are minimized.

FIG. 20 illustrates computer system hardware useful in implementing theembodiments discussed in FIGS. 1A through 19. FIG. 20 illustrates acomputer assembly useful as a processor configured to receivetemperature data from one or more flow characteristic sensors, forexample, temperature or pressure sensors, and determine how to adjust agas flow and/or temperature of the gas in order to change or maintainthe temperature of a patterning device to/at a desired level or range.The computer assembly may be a dedicated computer in the form of acontrol unit in embodiments of the assembly according to the inventionor, alternatively, be a central computer controlling the lithographicprojection apparatus. The computer assembly may be arranged for loadinga computer program product comprising computer executable code.

A memory 2001 connected to a processor 2023 may comprise a number ofmemory components like a hard disk drive (HDD) 2003, Read Only Memory(ROM) 2005, Electrically Erasable Programmable Read Only Memory (EEPROM)2007 and Random Access Memory (RAM) 2009. Not all aforementioned memorycomponents need to be present. Furthermore, it is not essential thataforementioned memory components are physically in close proximity tothe processor 2023 or to each other. They may be located at a distanceaway from each other.

The processor 2023 may also be connected to some kind of user interface,for instance a keyboard 2011 or a mouse 2013. A touch screen, trackball, speech converter or other interfaces that are known to personsskilled in the art may also be used.

The processor 2023 may be connected to a reading unit 2019, which isarranged to read data, e.g., in the form of computer executable code,from and under some circumstances store data on a data carrier, like afloppy disc 2017 or an optical disk 2015.

DVDs, flash memory, or other data carriers known to persons skilled inthe art may also be used.

The processor 2023 may also be connected to a printer 2021 to print outoutput data on paper as well as to a display 2029, for instance amonitor or LCD (Liquid Crystal Display), or any other type of displayknown to a person skilled in the art.

The processor 2023 may be connected to a communications network 2027,for instance a public switched telephone network (PSTN), a local areanetwork (LAN), a wide area network (WAN) etc. by means oftransmitters/receivers 2025 responsible for input/output (I/O). Theprocessor 2023 may be arranged to communicate with other communicationsystems via the communications network 2027. In an embodiment of theinvention external computers (not shown), for instance personalcomputers of operators, can log into the processor 2023 via thecommunications network 2027.

The processor 2023 may be implemented as an independent system or as anumber of processing units that operate in parallel, wherein eachprocessing unit is arranged to execute sub-tasks of a larger program.The processing units may also be divided in one or more main processingunits with several sub-processing units. Some processing units of theprocessor 2023 may even be located a distance away from the otherprocessing units and communicate via communications network 2027.Connections between modules can be made wired or wireless.

The computer system can be any signal processing system with analogueand/or digital and/or software technology arranged to perform thefunctions discussed here.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the present invention as described without departing fromthe scope of the claims set out below.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A patterning device support for controlling atemperature of a patterning device, comprising: a movable componentconfigured to move the patterning device, the movable componentcomprising: a gas inlet configured to supply a gas flow across a surfaceof the patterning device; a gas outlet configured to extract the gasflow; a gas flow generator configured to recirculate the gas flow fromthe gas outlet to the gas inlet; a duct in fluid communication with thegas inlet and the gas outlet and configured to pass the gas flow fromthe gas outlet to the gas inlet; and a movable component, configured tosupport and move the patterning device, comprising a short-stroke moduleand a long-stroke module at least partially surrounding the short-strokemodule, wherein the duct is coupled to the long-stroke module.
 2. Thepatterning device support of claim 1, wherein the duct forrecirculating, the gas flow comprises an outlet duct extending from thegas outlet to the gas flow generator, and an inlet duct extending fromthe gas flow generator to the gas inlet.
 3. The patterning devicesupport of claim 1, further comprising a temperature control elementconfigured to condition the temperature of the gas flow.
 4. Thepatterning device support of claim 3, wherein the temperature controlelement is downstream from the gas flow generator.
 5. The patterningdevice support of claim 1, wherein the gas flow generator comprises agas amplifier.
 6. The patterning device support of claim 5, wherein thegas inlet forms the gas amplifier.
 7. The patterning device support ofclaim 1, further comprising a temperature control element configured tocondition the temperature of a gas supply to the gas flow generator. 8.The patterning device support of claim 1, wherein: the duct for passingthe gas flow comprises an outlet duct and an inlet duct; the outlet ductcomprises a first branch extending from the gas outlet to the gas flowgenerator, and a second branch extending from the gas outlet to a secondgas flow generator; and the inlet duct comprises a first branchextending from the gas flow generator to the gas inlet, and a secondbranch extending from the second gas flow generator to the gas inlet. 9.A lithographic apparatus, comprising: an illumination system configuredto condition a radiation beam; a patterning device support configured tocontrol a temperature of a patterning device, comprising: a movablecomponent configured to move the patterning device, the movablecomponent comprising: a gas inlet configured to supply a gas flow acrossa surface of the patterning device; a gas outlet configured to extractthe gas flow; a gas flow generator configured to recirculate the gasflow from the gas outlet to the gas inlet; a duct in fluid communicationwith the gas inlet and the gas outlet and configured to pass the gasflow from the gas outlet to the gas inlet; and a movable component,configured to support and move the patterning device, comprising ashort-stroke module and a long-stroke module at least partiallysurrounding the short-stroke module, wherein the duct is coupled to thelong-stroke module; and a projection system configured to project thepatterned radiation beam onto a target portion of the substrate.
 10. Thelithographic apparatus of claim 9, further comprising a controllerconfigured to adjust a first characteristic of the gas flow to achieve adesired temperature of the patterning device.
 11. The lithographicapparatus of claim 10, further comprising: a sensor configured tomeasure a second characteristic of the gas flow, wherein the controlleris operatively coupled to the sensor and configured to adjust the firstcharacteristic of the gas flow based on the measured secondcharacteristic.
 12. The lithographic apparatus of claim 11, wherein thesecond characteristic comprises at least one of temperature, pressure,and flow rate.
 13. The lithographic apparatus of claim 10, wherein thefirst characteristic comprises at least one of temperature, pressure, orflow rate.
 14. A patterning device support for controlling a temperatureof a patterning device, comprising: a movable component configured tomove the patterning device, the movable component comprising: a gasinlet configured to supply a gas flow across a surface of the patterningdevice; a gas outlet configured to extract the gas flow; a gas flowgenerator configured to recirculate the gas flow from the gas outlet tothe gas inlet; and a duct in fluid communication with the gas inlet andthe gas outlet and configured to pass the gas flow from the gas outletto the gas inlet, wherein the gas flow generator comprises a pump,wherein the pump is configured to be driven by at least one of: a fan,the fan being driven by external gas flow caused by a scanning motion ofthe patterning device support, and a piston, the piston being driven byinertia caused by a scanning motion of the patterning device support.